Conventional ink cartridges for inkjet printers have an ink containing design which may be classified in three types: foam material, air bag and ink bag. Foam material has good space adaptability and is applicable even in a small space. It also is easy to install. Thus it has attracted a lot of interests in the industry.
Refer to FIG. 1 for the structure of a conventional ink cartridge that uses foam material. It includes a shell 1, a cap 2 located above the shell 1 and an inkjet head 3 located below the shell 1. The shell 1 has an ink compartment 4 to contain foam material 5 and ink. The inkjet head 3 has a boss 6 extending into the ink compartment 4. Conventional foam material 5 usually is a rectangular sponge squeezed into the ink compartment 4 from the upper side of the shell 1. The bottom of the foam material 5 is bucking against the boss 6 to raise actual porosity (PPI, pore/inch, as shown in FIG. 2) and increase the capillary force of the foam material 5 nearby the upper side of the boss 6 thereby to channel the ink contained in the foam material 5 to move towards the inkjet head 3 to supply the ink to the inkjet head for printing. Due to the height of the boss 6 is closely related to the porosity on the part section of the foam material 5, design of the boss 6 for different ink cartridges has to constantly test and modify the dimension of the boss 6 to enable the inkjet head 3 to form an optimal capillary force. However, the ink cartridge is formed by molding, every modification of the boss. 6 involves mold modifications. It is a time-consuming and tedious process. Design alteration is difficult. Moreover, while the design enables the capillary force of the foam material 3 decreasing gradually from the upper side of the boss 6 to the remote end and generates a desired ink channeling effect, the foam material 5 located away from the upper side of the boss 6 or on the lateral sides does not have desired distribution of capillary force as the foam material 5 located on the upper side of the boss 6. This is especially true for the foam material 5 abutting the lateral side of the boss 6. As the foam material 5 is stretched by the boss 6, the porosity drops significantly. As a result, the effect of capillary force also decreases. And the foam material 5 located on the lateral sides and remote from the boss 6 cannot channel the ink smoothly to the inkjet head 3. Hence residual ink tends to occur to the foam material 5 on the lateral and remote sides.
Furthermore, put a rectangular sponge respectively in two ink cartridges, one having the boss 6 extended into the ink compartment 4 and another without the boss 6 extending into the ink compartment 4, the test results of the residual ink are as follows:
BossBossextended intowithout extending intothe ink compartmentthe ink compartmentCompression ratio2.53.02.53.0of foam (Times)Ink contents (C.C.)38.2141.538.4640.6Residual ink (C.C.)10.1210.5320.023.12Residual ink ratio (%)26.525.452.056.9
The results lists above indicate that with the boss 6 extended into the ink compartment 4, residual ink ratio is about 26%, while the residual ink ratio is 55% when the boss 6 is not extended into the ink compartment 4. It is obvious that the design of having the boss 6 extended into the ink compartment 4 can reduce the residual ink ratio.
Although the boss 6 can help to reduce residual ink ratio, design alteration involves mold modifications. Thus design alteration is difficult. Moreover, the foam material 5 on the lateral sides of the boss 6 tends to be stretched by the boss 6 and results in decreasing of porosity and disruption of the capillary force, residual ink forms in the disrupted area. Therefore there is still room for improvement regard the techniques to reduce residual ink.